The art of producing gemstones for use in jewelry and other decorative objects by cutting and polishing naturally occurring mineral deposits is an ancient one. Existing gemstones that are colored achieve the color by absorbing some of the incident visual light. The absorption is often due to impurities in an otherwise transparent material such as aluminum oxide. Other natural gemstones, such as diamonds, are intrinsically colorless, but achieve high sparkle and flashes of color by the refraction induced by the high refractive index of the material. All intrinsically colored existing gemstones achieve their perceived color by preferential absorption of some of the wavelengths of light in the range of 400 nanometers to 700 nanometers. By the term intrinsically colored is meant colors that are invariant with respect to viewing angle, and are not the result of refraction of the incident light.
In modern times various synthetic and enhanced gemstones have been manufactured by a variety of processes. Some of these processes are intended to produce copies of naturally occurring gemstones, or to enhance the color of otherwise less valuable gemstones. For example, exposure of some transparent, colorless minerals to various types of high energy radiation can cause the mineral to become absorbing and therefore colored. Alternately, various processes have been described to improve the durability of gemstones by applying an overcoat of a more durable material. For example, Mayer (U.S. Pat. No. 3,539,379) describes the deposition of a single layer of aluminum oxide to the exterior of a gemstone to improve hardness and scratch resistance, but with the specific additional intent of not changing the perceived color of the native gemstone. German patent DE 3708171 A1 and a German patent application describe the deposition of diamond like coating to improve the hardness of gemstones. Feller (U.S. Pat. No. 4,599,251) discloses a decorative object manufactured by forming a single layer of a metal oxide on a silicon surface. Neumiller (U.S. Pat. No. 4,793,864) discloses formation of an organic film on the surface of a gemstone for the purpose of protecting the gemstone against ultraviolet and infrared radiation, and for the purpose of cleaning the surface of the gemstone. The modification of a gemstone by deposition of one or more layers on the upper surfaces only is described in Austrian Patent 265718 (1968), Swiss Patent 410,498 (1961), and Swiss Patent 346,666 (1956).
Whether natural or synthetic, all prior art gemstones that are perceived as colored by the eye achieve the color by absorption of some of the incident light, (except for intrinsically colorless gems, such as diamonds, whose perceived colors are due to refraction at the surface of the stone). When light strikes the surface of such a colored gemstone, some portion of the incident light is reflected, and the remainder of the light is transmitted into the interior of the gemstone. Because all wavelengths of the incident light are reflected in substantially equal amounts, the reflected light has no perceived color other than that of the original incident light. Some wavelengths of the incident light that is transmitted into the interior of the gemstone are absorbed by the material of the gemstone. Those wavelengths of light not absorbed by the gemstone eventually pass out of the gemstone. Because the light that has passed through the gemstone is now deficient in certain wavelengths of light (compared to the light incident on the gemstone) the gemstone appears to the observer to have a color, said color being that produced by the complement of the wavelengths of light absorbed by the gemstone.
It is a further property of all prior art colored gemstones that the perceived color is invariant with the angle of incidence of light or of the position of the observer with respect to the gemstone with the exception of refraction affects as described above. Thus all prior art colored gemstones are monochromatic in that the light reflected from the surface of the gemstone is not colored, and the perceived color of the light transmitted through the gemstone is invariant with the angle of incidence of the light or the position of the observer.
It is a further property of all prior art colored gemstones that the perceived brilliance of the gemstone is less than that of a colorless gemstone such as a diamond. This lesser brilliance is an unavoidable result of the fact that the color of the gemstone is produced by absorption of a large fraction of the total incident visible light. Thus less total visible light is returned to the eye from a colored gemstone than from a colorless gemstone of the same size and cut. The lesser amount of total visible light leads to the colored gemstone as being perceived as of lower brilliance, or duller, than the corresponding colorless gemstone.
It would be of great advantage to provide colored gemstones with a perceived brilliance as high as that of a colorless gemstone. It would be of further advantage to have such a colored gemstone be polychromatic, and for the perceived color to be dependent on the angle of incidence of the illumination source.
It is a natural property of existing colored gemstones that the depth of color of a small stone is less than the depth of color of a larger stone of the same material and cut. This is a consequence of the fact that the path length of the light in the small stone is less than in the large stone, and by Beer's Law the amount of light absorbed in the smaller stone is less. Because for reasons of economy it is often desired to use very small gemstones in jewelry, the lesser depth of color of such small stones is a disadvantage. It would be of great advantage to provide colored gemstones in which small samples had the same depth of color as larger samples.
An object of the present invention is providing colored gemstones and decorative objects whose perceived color is polychromatic, and whose perceived brilliance is greater than that of prior art colored gemstones.
Another object of the present invention is providing colored gemstones and decorative objects whose perceived color is dependent on the angle of illumination and the position of the observer with respect to the gemstone or object.
Yet another object of the present invention is providing colored gemstones in which small stones have the same perceived depth of color as larger stones made of the same material.
Yet another object of the present invention is providing decorative objects of novel and beautiful appearance.
Additional objects and features of the invention will be made evident by the following description in which the preferred embodiments are set forth in detail in conjunction with the accompanying drawings.